Managing tablespaces and data files

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Managing Tablespaces and Data Files

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• Create and manage tablespaces using Oracle

Managed Files (OMF)

• Obtain tablespace information

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Tablespaces and Data Files

Oracle stores data logically in tablespaces and physically in data files.

• Tablespaces:

– Can belong to only one database at a time

– Consist of one or more data files

– Are further divided into logical units of storage

• Data files:

– Can belong to only one

tablespace and one database

– Are a repository for schema

object data

Database Tablespace Data files

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Types of Tablespaces

• SYSTEM tablespace

– Created with the database

– Contains the data dictionary

– Contains the SYSTEM undo segment

• Non-SYSTEM tablespace

– Separate segments

– Eases space administration

– Controls amount of space allocated to a user

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Creating Tablespaces

CREATE TABLESPACE userdata

DATAFILE '/u01/oradata/userdata01.dbf' SIZE 5M;

A tablespace is created using the command:

CREATE TABLESPACE

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Space Management in Tablespaces

• Locally managed tablespace:

– Free extents are managed in the tablespace.

– Bitmap is used to record free extents

– Each bit corresponds to a block or group of blocks.– Bit value indicates free or used.

• Dictionary-managed tablespace:

– Free extents are managed by the data dictionary.– Appropriate tables are updated when extents are allocated or deallocated.

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Locally Managed Tablespaces

• Reduced contention on data dictionary tables

• No undo generated when space allocation or

deallocation occurs

• No coalescing required

CREATE TABLESPACE userdata

DATAFILE '/u01/oradata/userdata01.dbf' SIZE 500M EXTENT MANAGEMENT LOCAL UNIFORM SIZE 128K;

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Dictionary-Managed Tablespaces

• Extents are managed in the data dictionary.

• Each segment stored in the tablespace can have a

different storage clause.

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Undo Tablespace

• Used to store undo segments

• Cannot contain any other objects

• Extents are locally managed

• Can only use the DATAFILE and EXTENT

MANAGEMENT clauses

CREATE UNDO TABLESPACE undo1

DATAFILE '/u01/oradata/undo01.dbf' SIZE 40M;

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Temporary Tablespaces

• Used for sort operations

• Can be shared by multiple users

• Cannot contain any permanent objects

• Locally managed extents recommended

CREATE TEMPORARY TABLESPACE temp

TEMPFILE '/u01/oradata/temp01.dbf' SIZE 20M EXTENT MANAGEMENT LOCAL UNIFORM SIZE 4M;

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Default Temporary Tablespace

• Specifies a database-wide default temporary

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Creating a Default Temporary Tablespace

• During database creation:

–

CREATE DATABASE DBA01

LOGFILE

GROUP 1 ('/$HOME/ORADATA/u01/redo01.log') SIZE 100M,

GROUP 2 ('/$HOME/ORADATA/u02/redo02.log') SIZE 100M,

DATAFILE '/$HOME/ORADATA/u02/undotbs01.dbf' SIZE 200

DEFAULT TEMPORARY TABLESPACE temp

TEMPFILE '/$HOME/ORADATA/u03/temp01.dbf' SIZE 4M

CHARACTER SET US7ASCII

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Creating a Default Temporary Tablespace

• After database creation:

• To find the default temporary tablespace for the

database query DATABASE_PROPERTIES:

ALTER DATABASE

DEFAULT TEMPORARY TABLESPACE default_temp2;

SELECT * FROM DATABASE_PROPERTIES;

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Restrictions on Default Temporary Tablespace

Default temporary tablespaces cannot be:

• Dropped until after a new default is made available

• Taken offline

• Altered to a permanent tablespace

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Read-Only Tablespaces

• Use the following command to place a tablespace in

read-only mode:

– Causes a checkpoint

– Data available only for read operations

– Objects can be dropped from tablespace

ALTER TABLESPACE userdata READ ONLY;

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Taking a Tablespace Offline

• Not available for data access

• Tablespaces that cannot be taken offline:

– SYSTEM tablespace

– Tablespaces with active undo segments

– Default temporary tablespace

• To take a tablespace offline:

• To bring a tablespace online:

ALTER TABLESPACE userdata OFFLINE;

ALTER TABLESPACE userdata ONLINE;

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Changing Storage Settings

• Using ALTER TABLESPACE command to change storage settings:

• Storage settings for locally managed tablespaces

cannot be altered.

ALTER TABLESPACE userdata MINIMUM EXTENT 2M;

ALTER TABLESPACE userdata

DEFAULT STORAGE (INITIAL 2M NEXT 2M

MAXEXTENTS 999);

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Resizing a Tablespace

A tablespace can be resized by:

• Changing the size of a data file:

– Automatically using AUTOEXTEND

– Manually using ALTER DATABASE

• Adding a data file using ALTER TABLESPACE

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Enabling Automatic Extension

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Manually Resizing a Data File

• Manually increase or decrease a data file size using

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Adding Data Files to a Tablespace

• Increases the space allocated to a tablespace by

adding additional data files

• ADD DATAFILE clause is used to add a data file

• Example:

ALTER TABLESPACE user_data

ADD DATAFILE '/u01/oradata/userdata03.dbf' SIZE 200M;

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Methods for Moving Data Files

• ALTER TABLESPACE

– Tablespace must be offline.

– Target data files must exist.

ALTER TABLESPACE userdata RENAME

DATAFILE '/u01/oradata/userdata01.dbf'

TO '/u02/oradata/userdata01.dbf';

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Methods for Moving Data Files

• ALTER DATABASE

– Database must be mounted.

– Target data file must exist.

ALTER DATABASE RENAME

FILE '/u01/oradata/system01.dbf'

TO '/u03/oradata/system01.dbf';

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Dropping Tablespaces

• You cannot drop a tablespace if it:

– Is the SYSTEM tablespace

– Has active segments

• INCLUDING CONTENTS drops the segments.

• INCLUDING CONTENTS AND DATAFILES deletes

data files.

• CASCADE CONSTRAINTS drops all referential

integrity constraints.

DROP TABLESPACE userdata

INCLUDING CONTENTS AND DATAFILES;

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Managing Tablespaces Using OMF

• Define the DB_CREATE_FILE_DEST parameter in one

of the following ways:

– Initialization parameter file

– Set dynamically using ALTER SYSTEM command

• When creating the tablespace:

– Data file is automatically created and located in

DB_CREATE_FILE_DEST

– Default size is 100 MB

– AUTOEXTEND is set to UNLIMITED

ALTER SYSTEM SET

db_create_file_dest = '/u01/oradata/dba01';

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Managing Tablespaces Using OMF

• Creating an OMF tablespace:

• Adding an OMF data file to an existing tablespace:

• Dynamically changing default file location:

• Dropping a tablespace includes deleting OS files:

CREATE TABLESPACE text_data DATAFILE SIZE 20M;

ALTER TABLESPACE text_data ADD DATAFILE;

ALTER SYSTEM SET

db_create_file_dest = '/u01/oradata/dba01';

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Obtaining Tablespace Information

Obtaining tablespace and data file information can be obtained by querying the following:

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Summary

In this lesson, you should have learned how to:

• Use tablespaces to separate data

• Create various types of tablespaces

• Manage tablespaces

• Manage tablespaces using OMF

• Obtain tablespace information

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